Quadrant 47:
— Images and text provided by Howard Eskildsen
Craters create chaotic scene
The first thing that enters my mind when I
view this part of the moon is: What a mess!
Rocky rubble litters both sides of the image
with a strange array of craters intermixed. In
between the rubble, dark lava plains course
from top to bottom of the central image, all
pocked and marked by craters and rays. The
craters themselves seem chaotically varied in
size, form and degree of disarray. How can
any sense be made of it all?
Starting with the craters, it is apparent that
some are quite old, while others are fresh and
new. The most noticeable young craters are
24 km-diameter Lalande, just to the right of
center, and 26 km-diameter Mösting at the
upper right. They are the largest youthful
craters on the image and show very little
wear. Their rims are well defined, and rays
radiate from them across lava and rubble
in all directions — Lalande’s rays being
the brightest. Only a few other smaller
craters have rays of any sort and all are quite small in
comparison. Mösting A, for example is only 13 km
in diameter, and the rest of the rayed craters are much
smaller.
In contrast, the larger craters on the image show
various degrees of wear. Schröter and Sömmering
in the upper right image have fragmented rims and
filled floors as do Bonpland, Parry and Guericke
on the lower left of the image. Additionally, the rims
of Ptolemaeus and Alphonsus are worn and scarred
by gouges known as Imbrium sculpture. The crater
Flammarion has nearly been obliterated. Other craters
such as Gambart, Tolansky and Davy formed after the
Imbrium event and have intact rims, but were nearly
filled by mare basalt lavas that also partly buried some
of the rocky rubble and “embay” the margins of the
rubble.
Another unusual, but not unique feature, is the Davy
Crater Chain in the lower right corner of the image.
Lunar tidal forces broke up the incoming object that
created the chain into a series of smaller fragments.
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The fragments spread apart slightly and then
machine-gunned themselves onto the surface in a
series of craters.
So the story of the area starts with a now-buried
surface in which massive impacts created the
large craters, such as Ptolemaeus, Flammarion,
Bonpland and others. Sometime later, a supermassive impact to the north of this image
created Mare Imbrium and sent mountains of
debris flying across the landscape. It buried or
scarred everything in its path leaving the debris
fields on both sides of the images and creating
the deep gouges known as Imbrium sculpture.
The cataclysm took only minutes to wreak its
devastation across the surface of the moon.
Lava flows emerged over long periods of time
through cracks created by the massive impact and
eventually flooded any low lying areas, filling
craters that existed both before and after the
massive Imbrium event.
Other objects then cratered the solidified basalt, but
their rays were since erased by space weathering over
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eons. Finally the youngest craters appeared from later
impacts, and their rays are still splattered like graffiti
across the landscape. As a final insult, the Davy chain
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pocked across the moonscape like a drive-by shooting,
and the area now appears quite chaotic, but for some
very good reasons.
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